In previous studies we have isolated the various enzymes concerned with polyamine biosynthesis in Escherichia coli and have defined and mapped the genes concerned biosynthesis in Escherichia coli and have defined and mapped the genes concerned with the biosynthesis of these enzymes. We have constructed mutants deficient in each of these steps and have prepared strains that cannot synthesize polyamines. The purpose of these studies is to find what the action of polyamines is in vivo, i.e., the physiological role of the polyamines. In our more recent studies we have found that these mutants are defective in the translation step in protein biosynthesis in vivo. We have found that changes in the S12 ribosomal protein resulting from a rpsL (strA) mutation cause a slow-growing polyamine-deficiet strain to cease growing; i.e., we now have an absolute polyamine-requiring auxotroph of E. coli. We have also shown a marke defect in the multiplication of amber mutants of bacteriophage T4 and T7 in polyamine-deficient strains and accumulation of an amber fragment. These results indicate that polyamines are involved in the stability or conformation of the ribosomal complex involved in protein biosynthesis in vivo. We have also constructed a plasmid containing the gene for adenosylmethionine decarboxylase that is suitable for DNA sequencing.